Help needed - mystery part that I can't find the spot for

[Crunchmeister]

It was a quick, solid grind for about 1/2 second, then the fuse blew. I tried bypassing the fuse, and nothing. Seems like something is jammed up hard. I'd guess it's inside the mechbox.

[CDN_Stalker]

Maybe a shim or two got misplaced and is causing the jamming?

[Crunchmeister]

I have the Modify Modular gear set (http://www.airsoftparts.ca/store2/in...roducts_id=687) that comes as a single unit, already "correctly" shimmed. I don' think shimming is the problem.

[CDN_Stalker]

Hmm, I've wondered if that gearset is compatible with ALL types of mechboxes, or if there are a couple that would fit tighter than others. I've found in the past reshimming is needed when installing new gears, new bushings or even a new mechbox (of a different type for all those).

Doubt that's your problem, but something is going on in there.

[Crunchmeister]

Well, it says it's compatible with TM V2/V3 mechboxes, so I assumed it would be. There's no option to reshim on this gearset. It's a pre-assembled modular unit. I tried installing just the gears and closing up the mechbox and manually spinning the gears, and they seemed to move pretty smoothly and freely. When I reassembled, with the cylinder, etc, I made sure the tappet plate notch on the sector gear was in the 1 oclock position to adust the gear timing too.

Hmmm... mysteries. Not sure if I'll have time to mess with it today or not though...

[CDN_Stalker]

Ya, TM V3/V3 mechboxes, but if it's a mechbox of another type (say an aftermarket reinforced one or something), it might not be shimmed properly, aka. too tight. I'd tend to trust that gear set in a stock TM gun, but don't like the fact it can't be shimmed for adjustment if used in another type of mechbox shell.

Open your mechbox, take out the cylinder, tappet plate, etc. then put a few screws in and snug them down, then spin your gears by pushing on the sector gear. If it doesn't turn easily and smoothly, then there is somethig wrong with the shimming of that gearset.

[Crunchmeister]

Thought I would update this with new info...

I halted my work on the gun for a while due to lack of time, plus I was expecting the arrival of a metal C8 body. I got the body last week, but didn't have time to install it. Finally tonight I stripped the gun down and started building it again with its new metal body. And I once aggain pulled the mechbox apart to try to find what was wrong.

I discovered why my mechbox was locking up. When I had 'tested' it with only the gears last time, I had only closed it up with a couple of screws. I followed your advice, CDN_Stalker. I opened it and stripped it of the cylinder & piston assemblies, and reassembled it with only the gears. But this time, I installed all the screws on the box this time. I couldn't turn the gears manually. They were seized tight

I took it apart again to see what was wrong. Turns out it was the bushings that weren't completely seated into the mechbox. I noticed they weren't quite flush with the inside of the mechbox. I couldn't manually push them in further, so with a wooden dowel and hammer, I lightly tapped them in all the way till they were flush and reassembled and closed the mechbox without the spring / cylinder assemblies, but again, with all the screws. The gears worked like a charm. They spun freely and smoothly.

I also followed Lupo's advice on the piston head, and was able to successfully remove the piston head and stock spring, and installed the new Prometheus spring. I was able to reassemble the mechbox without any further issues. I mounted the mechbox back into the lower receiver, installed the grip and motor, and connected the battery to test fire it. It worked perfectly with an excellent rate of fire - faster than its former ROF, I believe.

Now, the problems arose when I installed the upper receiver. Once I got the whole gun reassembled it would no longer fire. I didn't feel like troubleshooting it tonight (getting late), so I'll probably check it out on the weekend again when I have some free time. But barring this new incident, so far so good, when it comes to solving problems. This repair and upgrade has been a challenging process so far, but I've learned so much about my gun. Despite the problems, it's been a great learning experience to date and a positive one at that. I realize until it's full assembled and functional, I'm not out of the woods quite yet.

I'm glad I decided to take on this repair and upgrade myself so I can learn how to do this on my own, rather than having to rely on a gun doc every time I have a problem or want to upgrade. And with awesome advice from knowledgeable people on this forum, I think I'll be able to complete this project successfully. Thanks for the help so far. And I'm sure I'll be picking your brains again down the road with other problems.

So here's what the gun looks like at the moment...